JPS6131867B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photographically produced stencil (abbreviated as a photographic stencil) for use in screen printing.
Regarding.

In screen printing, the image to be printed is defined by covering all or part of the screen printing mesh with a stencil material. Thus, during printing, the stencil material prevents screen printing ink from passing through the shielded area.

Although this stencil can be produced by hand, it is usually produced photographically in practice. The production of this photographic stencil consists of a dry water-soluble photopolymer layer which, upon image exposure to suitable light, becomes water-insoluble in the exposed areas such that the layer material in the unexposed areas is washed away with cold or hot water to produce a photographic stencil. It is necessary to prepare The photosensitive layers used in screen printing are generally based on polyvinyl alcohol, polyvinyl alcohol-polyvinyl acetate mixtures or gelatin and are sensitized with water-soluble dichromates, diazonium salts or ferric salts.

Two different methods are used to apply photographic stencils to screens: the direct method and the articulatory method.
In the direct method, an aqueous polyvinyl alcohol solution is mixed with an aqueous emulsion of ordinary polyvinyl acetate, a sensitizer is added, and a viscous liquid containing about 10-30% by volume of non-volatile substances is coated on a screen under tension and dried by evaporation. Let it happen. Since drying substantially reduces the thickness of the layer, several coats are typically applied with each intermediate drying to provide a photographic stencil of sufficient thickness to provide the dried layer with adequate mechanical strength. The dry sensitized mesh is exposed in contact with a high contrast photographic positive in a vacuum frame so as to bring it into intimate contact with the positive. The exposing light may be mercury metal halide, mercury vapor, pulsed xenon or carbon arc light, all of which have high intensity in the 350-450 nm range where the sensitized polymer is most sensitive. The image is carefully washed away with cold or hot water to remove the unexposed polymer, developed, and then the remaining polymer is dried again to produce a photographic stencil.

In the indirect method, an aqueous solution of the sensitizing polymer, usually at a concentration of 10-25% by volume, is coated in a thick layer onto a colorless transparent film substrate, such as a polyester film.
This is coated for later dry stripping. After a long drying step in a complex drying tunnel, the dried polymer layer is exposed to a high-contrast photographic positive in a vacuum frame using the same light beams as in the direct method. The image is developed by rinsing off the water-soluble unexposed polymer with cold or hot water, and while wet the polymer still remaining on the film substrate is pressed with light pressure against the screen steel and allowed to dry. Finally, the film base material is peeled off, leaving the printing stencil on the steel grain.

Therefore, both direct and indirect methods of photographic stencil production require at least two long drying steps with careful adjustments to avoid drying defects and dust contamination.
The finished stencil does not withstand water-based screen inks or inks containing hydroxyl groups and organic solvents. Since water-based screen inks are widely used for textile printing on flat and cylindrical screens, the stencils must be protected by either chemical hardening or baking onto a protective lacquer.

Furthermore, evaporation of water during the first drying step of the direct method causes shrinkage and deterioration of image quality, especially the formation of sawtooth edges due to defective bridging of the openings. Multiple coats with intermediate drying generally reduce this effect, but limited print detail definition is still obtained with the direct method. The indirect method also suffers from deterioration in printing quality due to shrinkage, but the main problem is that the stencil is applied to the eyes in an expanded state rather than in a liquid state, so the adhesion is low because it does not cover the eyes. Both polyvinyl alcohol and gelatin have low specific adhesion to polyester single fibers, which are most widely used in screen printing.

According to the present invention, one side of a screen network supported under tension is brought into contact with a light-transmissive sheet material and a photopolymerizable liquid composition is applied to the other side, so that the network is substantially coated with the liquid composition. imagewise exposing a net filled and coated with the liquid composition through the sheet material to polymerize the composition on the net in exposed areas, and separating the sheet material from the net to remove the liquid composition remaining in unexposed areas. A method of making a stencil for screen printing is provided, the method comprising forming a stencil for use in screen printing by substantially removing the polymeric composition and leaving the polymerized composition on the screen in exposed areas.

The method of the present invention allows the production of high-quality photographic stencils quickly with simple equipment, without the need for special techniques, without the generation of waste fluids, or without the need for the use of hazardous chemicals such as dichromates and diazonium salts. can be manufactured. Another important advantage of the method of the invention is that the photopolymerizable liquid is substantially non-volatile;
There is no need to carry out a drying process in the production of the photosensitive layer. A suitable layer thickness can therefore be obtained in one coating operation. This is because a screen coated with a sensitized polyvinyl alcohol solution, for example, is exposed before drying (i.e. while still wet, liquid) and can be used as a photographic stencil, since no water-insoluble exposed layer is available for adhesion to the eye. This is in contrast to conventional methods that cannot be used to produce. Exposure and development with water is possible only after drying of the coating.

However, according to a preferred embodiment of the invention, one side (printing side) of the screen is in contact with the light-transmissive sheet material, and the opposite side of the screen is coated with a photopolymerizable liquid composition so that the image Exposure is made through the sheet material and the stencil is developed by separating the sheet material and the stencil so that the unexposed liquid composition remains on the sheet material. The light-transmitting sheet, also called protective film, may be a plastic film, such as a transparent polyester or polypropylene film, or glass.

The coated screen is exposed to the projection beam or by contact between the photographic positive in the printing frame and the protective film. In the latter case a protective film prevents the positive from coming into contact with the liquid. After exposure, the protective film is easily removed and the stencil is developed. Most of the unexposed liquid adheres to the film and is removed along with it. After the coated screen is exposed in direct contact with the photographic positive, if the positive is of a suitable material, it can be peeled off and the stencil developed.

After peeling off, the openings on the bottom of the printed (unexposed) part are essentially open, so the screen can be used for printing immediately. When the screen is open, as in normal screen printing, a thin film of the liquid composition usually remains on the surface of the fibers, but this thin film is dissolved or dispersed in the screen ink during the first few prints. do. Separately〓
The thin liquid film on the fiber can be removed using a liquid solvent or dispersant before printing. Yet another method is
The liquid is re-exposed to a uniform beam of light to polymerize the liquid and fix the residual liquid onto the fibers. This fixing method is
It is valuable if it is necessary to reduce the aperture somewhat and reduce the amount of ink applied to the screen.
The fixation method also strengthens the image edges of the photographic stencil and increases the strength of the photographic stencil.

A further important advantage of the protective film peel-off method is that a proof of the stencil is produced on the film. The photopolymerizable liquid can be colored with pigments or soluble dyes to facilitate inspection of the resulting photographic stencil to facilitate inspection of the coating operation. Therefore, after removal, the liquid print on the film is similarly colored and visible. This liquid print can polymerize by exposure to uniform light and become a true proof of a photographic stencil, which is a copy of the print that would be obtained by printing the stencil.

By using photopolymerizable liquids in the appropriate colors, i.e. yellow, magenta, cyan and black, the underprints can be used for four-color intercolor printing in which the underprints are superimposed in progressive colors, resulting in a final full color. A set of colored underprints is obtained from these four photographic stencils. This is of great value to printers in adjusting color print densities.

When exposed in contact with the positive in a vacuum frame, the same second protective film is placed on top of the frame so that the rubber blanket of the frame does not come into contact with the photopolymerizable liquid in the opening. Both protective films can be peeled off for development. Alternatively or additionally, a fine powder such as silica airgel or talc can be applied to the top surface of the rubber blanket to prevent contact.

The method of the invention applies to monofilament and multifilament polyesters, polyamides, stainless steel, phosphor bronze, nickel, silk and organdy (cotton).
Can be used for various screens including 〓
The material may be woven, knitted or non-woven, or may be a perforated metal or plastic material, or may be electrically made or etched. Photographic stencils on both flat and cylindrical screens can be produced by the method of the present invention, or conventional conventional screen printing methods can also be used.

The photopolymerizable liquid composition is polymerized into a solid upon exposure to suitable light, such as ultraviolet or visible light or a mixture thereof. In general, visible light and light close to ultraviolet light are produced using mercury vapor lamps,
Sensitivity to mercury metal halides, pulsed xenon, and carbon arcs is preferred because it is easily generated and relatively safe to use.

By appropriately selecting the components of the liquid photopolymerizable composition and the thickness of its layer, strong adhesion to the screen can easily be obtained, resulting in a photographic stencil suitable for long-term printing. The thickness of the photographic stencil can be easily adjusted within a wide range by adjusting the thickness of the liquid photopolymerizable layer applied to the stencil. When the film is wrapped in a photopolymerizable material, an extremely strong photographic stencil can be obtained by mechanical attachment. Because the method of the present invention eliminates the need for drying of the photopolymerizable liquid layer, there is little shrinkage from the original layer. Depending on the coating method used, the liquid layer can be instantaneously coated on both sides of the base, lower than the base, or coated on one or both sides of the base, higher than the base. Strong adhesion of photographic stencils to paper is obtained through the use of special photopolymerizable compositions, particularly acrylated urethanes and compositions which, through adjustment of cross-linking density, provide flexible photographic stencils with high tensile strength.

Preferably, the photopolymerizable liquid composition used in the present invention is comprised of ethylenically unsaturated monomers or prepolymers or mixtures thereof. Ethylenically unsaturated prepolymers have polymerizable components in their molecules. It is highly desirable to use rapidly photopolymerizable materials to reduce exposure time to light.

The rapid photopolymerization reaction is photoinitiated on monomers and prepolymers with terminal or attached acryloyl or methacryloyl groups: _CH2 =CR-CO-, where R represents H or _CH3 , respectively. It is obtained by a vinyl addition polymerization reaction. Acryloyl groups undergo a faster polymerization reaction than methacryloyl groups. References to acryloyl groups below also include methacryloyl groups.

For a photopolymerizable liquid composition to have good coating properties, it is necessary to have an appropriate viscosity, generally from 2 to 50 poise, preferably from 10 to 30 poise, depending on the molecular weight and composition of the photopolymerizable material. Easy to adjust.
High viscosity prepolymers can be conveniently mixed with low viscosity monomers for precise viscosity adjustment.

The low-viscosity photopolymerizable liquid substance is a substance without a polymerizable group in its molecule, a monomer, and suitable substances include esters of acrylic acid or methacrylic acid and monohydric or polyhydric alcohol, especially There are acrylate esters of monohydric, dihydric, trihydric and tetrahydric alcohols. Monomers with very low volatility and minimal skin and eye irritation are preferred; this property is generally obtained with high molecular weight monomers. The following examples of acrylate esters of alcohols are suitable.

Monohydric alcohol: 2 phenooxyethanol, 2
- Phenoxyethoxyethanol and their hydrogenated derivatives: Dihydric alcohols: tripropylene glycol, bisphenol A, hydrogenated bisphenol A and hydroxyethyl ethers and hydroxypolyethoxy of bisphenol A and hydrogenated bisphenol A and propoxyethers: Trihydric alcohol: Trimethylolpropane: Tetrahydric alcohol: Pentaerythritol: Polyhydric alcohol: Dipentaerythritol.

All hydroxyl groups are esterified or 1 or 2
The above groups may remain unesterified and the free hydroxyl groups may further or partially react with mono-, di- or tri-isocyanates to form urethanes.

High viscosity is about 250− between high viscosity liquid and solid.
It is easily obtained with a photopolymerizable prepolymer having a molecular weight of 5000. Terminal or appended acryloyl groups can be incorporated into polymerizable components such as polyurethanes, polyepoxides, polyethers, polyesters, and polyaminoformaldehyde polymers.

Generally acryloyl groups 2-9, preferably 2
-4 can be incorporated into the polymer molecule, for example by reacting acrylic acid or acryloyl chloride with a polymer or polymerizable material containing free hydroxyl groups. This group can also be used to convert hydroxyalkyl acrylates into isocyanates, epoxides,
It can also be added by reacting with a polymer or polymerizable substance having carboxylic anhydride or aminoformaldehyde groups.

For example, an acrylated epoxy prepolymer is produced by reacting a bisphenol A polyglycidyl ether with a terminal epoxide group with acrylic acid that opens the oxirane ring, and then reacting the resulting hydroxyl group with acryloyl chloride to add an additional acryloyl group. .

Acrylated urethane prepolymers are produced by reacting, for example, hydroxyethyl or hydroxypropyl acrylate with hexamethylene di-isocyanate or other di- or poly-isocyanates, and then converting the terminal isocyanate groups into polyethers or polyesters having further hydroxyl groups. It is produced by reacting with

Alternatively, acryloyl polyether urethanes and acryloyl polyester urethanes can be prepared by reacting excess di- or poly-isocyanate with a polyether or polyester having free hydroxyl groups and then reacting this polymer with a hydroxyalkyl acrylate.

To obtain well balanced properties, two or more monomers and two or more prepolymers are used in the photopolymerizable liquid composition. In addition, in order to initiate the photopolymerization reaction, one or more photoreaction initiators are added to the composition in an amount of 0.01 to 30% by weight, usually 1 to 30% by weight, based on the weight of the unsaturated substance.
Dissolve or disperse at a concentration of 10% by weight. The following are examples of photoinitiators: ketones and benzophenones, 4,4'-di-methyl-aminobenzophenone, acetophenone, 2,2-diethoxyacetophenone, halogenated benzophenones, benzyl, benzyl. Derivatives such as dimethyl acetal.
Acryloins and derivatives such as benzoin, benzyl dimethyl acetate and benzoin isopropyl ether. Thio compounds such as thioxasone, 2-chlorothioxasone, benzoyldiphenyl sulfide, polynucleaquinone and derivatives such as benzoquinone, chloroanthraquinone. Diazo compounds, including fluoroborate salts of chlorinated hydrocarbons and diazonium compounds, such as hexachloroethane.

The effectiveness of photoinitiators is enhanced by the inclusion of tertiary amines such as ethyl dimethyl-aminobenzoate or aminoacrylate polymers.

Other types of unsaturated monomers and polymers, such as N-vinylpyrrolidone, vinyl acetate, allyl and cinnamyl esters, (N-isobutoxymethyl ) Acrylamide derivatives such as acrylamide, triallyl cyanurate can be added. Unsaturated polyesters include maleate, fumarate, itaconate and citraconate esters of glycols.

The main photopolymerizable material is a non-reactive polymer, such as a high acid number polyester to provide alkaline solubility to the photopolymerized photographic stencil, or a dispersed finely divided polyvinyl chloride that solvates during the photosynthesis reaction to increase film strength and flexibility. It is also possible to disperse or dissolve the vinyl chloride-acetate copolymer.

Finally, various additives can also be added to the photopolymerizable compositions, such as pigments, fillers, flow agents and waxes.

The photopolymerization reaction is inhibited by atmospheric oxygen, which acts primarily on the outer surface of the layer. Although this results in a reduction in film strength, oxygen suppression can be prevented in the present invention by the use of a protective film that prevents the access of atmospheric oxygen over the liquid composition upon exposure.

Many properties of photographic stencils, such as solvent resistance, flexibility, tensile strength and Young's modulus, are affected by crosslink density.

Cross-linking density is primarily determined by the number of ethylenically unsaturated photopolymerizable groups per molecule of the material used in the liquid composition, called "reactivity." One ethylene group per molecule cannot cross-link and produces a soft, highly stretchable photographic stencil. Two ethylene groups per molecule generally produces a strong photographic stencil that is flexible, while three ethylene groups produces a stencil with a high Young's modulus and is not flexible.
It is convenient to mix substances with 1, 2 and 3 ethylene groups to obtain a cross-linking density that will be the average value.

Flexibility is also due to long alkyl chains in the photopolymerizable material,
They are obtained using flexible chemical groups such as polyester and polyether groups in conjunction with control of cross-linking density.

In general, 2-reactive materials, ie, materials with two acryloyl groups per molecule, provide the most balanced properties. Mixing mono-acrylates and tri-acrylates or higher acrylate materials is another method of crosslinking density adjustment. In this mixture, the unsaturated monomer, prepolymer or mixture thereof must have an average of 2 to 3 acryloyl groups per molecule. Flexible stencils generally have very high adhesion and are commonly used in screen printing. High coefficient values are useful for improving the dimensional stability of cylindrical printing screens.

In screen printing operations, it is desirable to remove the photographic stencil after printing and reuse the screen. In the present invention, this can be done in a variety of ways. Non-photopolymerizable materials with special solubility can be mixed into the liquid composition. A low molecular weight polymer with a high acid value due to a high content of carboxylic acid groups, such as polyvinyl phthalate or mellitic anhydride glycerol polyester, is dissolved in a photopolymerizable liquid composition and the photopolymer formed thereon is alkalised. It is made soluble or dispersible in an aqueous solution. Separately or additionally, a photopolymerizable high acid value substance such as acrylic acid may be mixed into the photopolymerizable liquid to make it alkali soluble.

2 such as di-acrylate monomers and di-acrylate prepolymers to adjust the cross-linking density.
- The predominant use of reactive materials produces photopolymerizable stencils that are soluble in or soften in special solvents such as methylpyrrolidone and ketones.
Softened photographic stencils can be removed by spraying with high pressure water at 500 to 1000 psi.

The present invention also provides a stencil for use in screen printing made by current methods.

The present invention further provides a method of screen printing that includes delivering screen printing ink to a substrate through such a stencil.

The invention is illustrated in a schematic diagram in the accompanying drawings.

Figure 1 shows an enlarged cross section of a single fiber 1.
A transparent plastic film 3 is coated with a photopolymerizable liquid 2. The photo positive 4 has a high-density image 5 and is placed in contact with the coated film, and when exposed to light rays 6, the light causes a photopolymerization reaction of the liquid.

Attached Figure 2 shows the development of the exposed part of Figure 1, in which the exposed material was converted into a solid state and remained inside to form the photographic stencil 7, but most of the unexposed liquid 2 was made of plastic. It has been removed together with film 3. A thin layer of unexposed liquid 8 remains on the surface but is removed by washing with a solvent or dispersant, or removed from the screen by the ink passing through it in the first few prints. . Alternatively, the liquid 8 may be photopolymerized on the surface so as to reduce the aperture of the surface by exposing the surface to a homogeneous beam of light.

The invention is further illustrated in the following examples.

Example 1 A foam rubber sheet with a thickness of 3 mm was placed on a flat table, and a clean transparent polyester film with a thickness of 50 μm was placed thereon as a protective film. A printing screen made of taut plain-woven polyester with a fiber diameter of 40 μm and 120 meshes per centimeter was placed on the film with the lower side (printing side) of the screen in contact with the polyester film.

The following composition (parts by weight): 1 Acrylated urethane 65.08 2 Trimethylolpropane triacrylate
12.6 3 Phenoxyethyl acrylate 18.0 4 Dimethoxyphenylacetophenone 3.6 5 4,4'-dimethylaminobenzophenone 0.27 6 Phthalocyanine blue pigment 0.45 100.00 (Component 1 is hydroxyethyl acrylate and hexamethylene di-isocyanate The three-color blue light polymerizable liquid obtained by the reaction of the isocyanate group and the hydroxyl group-containing polyester, and components 4 and 5 are photoinitiators) was rolled into a liquid ball with a hard rubber roller. Gently spread it on the screen to coat the surface. The openings were completely filled with liquid and the liquid was flush with the surface, resulting in an accurate and uniform coating weight adjusted by physical measurements. If air bubbles form in the coating, the coating operation is carried out with the flat table tilted or even vertical, and the coating started from the bottom. You can also move the rubber roller back and forth several times to remove air.

This screen was used as a light source and exposed for 6 minutes to a high contrast photographic image using a 2 Kw mercury metal halide lamp with peak light in the 400-450 nm band.

Separately, a high contrast photographic halftone positive was placed in contact with a protective film and placed in a vacuum exposure frame. Second
A protective polyester film was placed on the top surface. This screen is 2Kw at a distance of 1 meter.
The screen was exposed to a mercury halide lamp under vacuum for 4.5 minutes and the screen was removed from the vacuum frame.

Then, the two polyester films were peeled off from the film. In the black opaque areas of the photographic positive where no light was exposed on the intensifying screen, the composition remained liquid and was removed along with the polyester film, resulting in a positive working process. Thus, the polyester film had a fine blue image. The image on the polyester film from the bottom surface is re-exposed for 4 minutes from the same light source without a photographic positive, whereby the liquid turns into a hard layer and adheres strongly to the polyester film, making it an excellent proof for photographic stencils. Ta.

Cyan pigments can be used to produce color proofs suitable for cyan printers with three or four intercolor sets, and also to form photographic stencils that are clearly visible on screens. Yellow, magenta, and black pigments or soluble dyes can be used in the photopolymerizable liquid in place of cyan pigments if photographic stencils of other colors in the four-color intercolor set are to be made.

After stripping, some of the blue liquid remaining on the fiber surface can be removed by washing the screen with isopropanol, but the screen can be used as is for printing. The first print will clean the fibers with the liquid film.

Instead of using a polyester protective film on the underside, a photographic positive can be used, or after removal, the liquid composition can be removed with a solvent such as 2-ethoxy-ethanol without damaging the positive.

Example 2 The screen printing material of Example 1, which had been dyed deep yellow with a yellow disperse dye, was stretched and fixed on a screen frame. Photographic stencils were made as described in Example 1, except that the exposure was increased by 50% to compensate for light absorption by the yellow color.

Proofs on polyester film were found to have improved precision in highlight points and fine line details, with yellow strongly absorbing actinic light scattered by the diaphragm and reduced light scattering by the diaphragm. .

Example 3 A screen frame covered with the monofilament polyester of Example 1 was placed on the transparent polyester protective film of Example 1 or the glass plate of the vacuum exposure frame. The following composition was then applied onto the surface using a hard rubber roller. (Parts by weight) 1 Di-acrylate ester of bis-hydroxyethyl ether of bisphenol A 90 2 Reaction product of pentaerythritol diacrylate and hexamethylene diisocyanate 5 3 Benzyl 2 4 4,4'-dimethylaminobenzophenone 3 100 (Component 1 is a 2-reactive acrylated liquid monomer and component 2 is an acrylated urethane prepolymer with 4 acrylate groups per molecule. Components 3 and 4 are photoinitiators.) Composition viscosity was 15-20 poise. A clean second polyester protective film was placed on top of the surface.

A high contrast photographic positive was placed below the surface with its emulsion side in contact with a protective film and exposed for 3 minutes to a 2 Kw mercury metal halide lamp peaking at 400-450 nm in a vacuum printing frame. The top protective film was removed and discarded, the bottom protective film was removed and the photographic stencil was developed.

When printing with a solvent-based screen ink containing 2-ethoxyethanol as a solvent, the residual photopolymerizable liquid material on the yarn was removed after the first 2-3 prints.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of a single fiber coated with the photopolymerizable liquid of the present invention. Attached FIG. 2 is a diagram showing the development of the 〓 of attached FIG. 1 coated with the photopolymerizable liquid of the present invention and exposed. Numbers in the figure: 1...Single fiber, 2...Photopolymerizable liquid, 3...Transparent plastic film, 4...
Photo positive, 5...image, 6...ray of light.

Claims (1)

[Scope of Claims] 1. One surface of a screen network supported under tension is brought into contact with a light-transmissive sheet material, and a photopolymerizable liquid composition is applied to the other surface, so that the network is substantially coated with the liquid composition. imagewise exposing a screen filled with liquid composition and coated with the liquid composition through the sheet material to polymerize the composition on the screen in the exposed areas, and separating the sheet material from the screen to remove the remaining liquid composition in the non-exposed areas. 1. A method for making a stencil for screen printing, which comprises forming a stencil for use in screen printing by substantially removing material and leaving a polymerized composition on the screen in exposed areas. 2. The method of claim 1, wherein the sheet material is a flexible, light-transparent plastic film. 3. A method according to claim 1 or 2, wherein the light-transmissive sheet material has light-opaque areas that provide image exposure when uniformly irradiated. 4. The method according to any one of claims 1 to 3, wherein any residual unexposed liquid composition remaining on the screen after the sheet material is removed is washed away with a composition solvent or dispersant. 5. Any residual unexposed liquid composition remaining on the screen after removing the sheet material is left on the screen for removal during use of the stencil by printing with an ink that dissolves or disperses the liquid composition. The method according to any one of claims 1 to 3. 6. A method according to any of claims 1 to 5, wherein the coated mesh is imaged exposed to ultraviolet or visible light. 7. The liquid composition is colored so that the liquid remaining on the sheet material after separation from the screen is
7. A method according to any one of claims 1 to 6, resulting in a stencil indicia which is polymerized upon exposure. 8. A method according to any one of claims 1 to 7, wherein the liquid composition has a viscosity of 2 to 50 poise. 9. A method according to any one of claims 1 to 8, wherein the liquid composition comprises a photopolymerizable ethylenically unsaturated monomer or prepolymer or a mixture thereof. 10. The method of claim 9, wherein the unsaturated monomer or prepolymer has pendant or terminal acroyl or methacryloyl groups. 11. The method of claim 10, wherein the majority of the unsaturated monomers or prepolymers in the liquid composition have two acryloyl groups per molecule. 12. The method according to any one of claims 9 to 11, wherein the unsaturated monomer, prepolymer or mixture thereof has an average of 2 to 3 acryloyl groups per molecule. 13. The method according to any one of claims 9 to 12, wherein the liquid composition contains an unsaturated substance with a molecular weight of 250 to 5000. 14. The method according to any one of claims 1 to 8, wherein the liquid composition comprises an ester of acrylic acid or methacrylic acid and a monohydric or polyhydric alcohol. 15. The liquid composition contains a photoinitiator for increasing the photopolymerization reaction rate of the composition to ultraviolet rays or visible light or a mixture thereof, and the coated net is imagewise exposed to ultraviolet rays or visible light or a mixture thereof. A method according to any one of claims 1 to 14.